IDE DMA under 2.4?

i've noticed that i can't seem to enable DMA on my IDE disk under 2.4.2-ac18. this works under 2.2.19pre14 (the last 2.2 kernel i built). i've been slogging through lk archives but can't seem to find where this got changed.

when i do 'hdparm -d 1 /dev/hda', i get
/dev/hda:
setting using_dma to 1 (on)
HDIO_SET_DMA failed: Operation not permitted
using_dma = 0 (off)

my controller is a PIIX4, the disk is an IBM DJSA-220 (2.5" laptop drive, 20GB).

is there any way to reenable DMA on this disk? according to 'hdparm -t -T' while booted single-user, i get about 6MB/s without DMA (under 2.4), and about 17MB/s with (under 2.2).

tia, and sorry if it's a faq i couldn't dig up,
ian

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Ian Soboroff                                       [email protected]
University of MD Baltimore County      http://www.cs.umbc.edu/~ian